The bracket is of the type for use in the ribbon arch technique. This is a technique which allows an arch-wire to be inserted into the bracket in a vertical direction, as opposed to the edgewise technique in which the bracket has a slot opening horizontally for arch-wire insertion.
With reference to the prior art Specifications known to Applicant, the bracket of Hanson in U.S. Pat. No. 4,698,017, there is disclosed a tie-less bracket for the edgewise technique with a spring clip and uses arch-wires of different cross section.
Klapper U.S. Pat. No. 4,676,746 uses the principles of pre-torquing and pre-angulation and pre-rotation, but requires a three-piece assembly of interchangeable parts.
In my earlier Australian Patent No. 490821, there is disclosed the provision of a base portion having an undercut base which is similar to that disclosed in the Klapper Specification referred to above.
There is also disclosed in U.S. Pat. No. 4,659,309 by Merkel a pre-torqued-preangulated edgewise bracket with a rhomboidal shape. This bracket, together with other edgewise brackets, have sharp corners which are likely to lead to less patient comfort in the mouth and greater resistance to the passage of food.
The Fujita bracket disclosed in U.S. Pat. No. 4,655,708 is a bracket adapted to be applied to the lingual, or tongue, surface of the tooth whereas the present bracket is intended to be applied to the labial or cheek side of the tooth.
The Fujita bracket being a lingually placed bracket has a variable slot position which could include a ribbon arch or vertical insertion presumably from the occlusal side. The Fujita bracket slot has no specific angularity therein and this could lead to inaccuracies in torque angle resulting in a lower standard of finish.
The ribbon arch (Begg brackets demonstrated by Johnston in U.S. Pat. No. 3,408,739 and Kesling in U.S. Pat. No. 3,178,821 illustrate the appliances used in recent years reintroducing the ribbon arch approach to contemporary orthodontics. The main difference between the modern (Begg) technique and the original ribbon arched method is that the modern technique uses a round wire, not a rectangular wire. The Johnston bracket can achieve a lengthening of the archwire slot by the use of an auxiliary device called a "stabilizing bar".
Similarly, Forster discloses in U.S. Pat. No. 4,268,249 a ribbon arch bracket which employs an auxiliary like that of Johnston mentioned above. Forster's bracket can take a rectangular arch-wire, but has no provision for pre-torquing. Kesling in his U.S. Pat. No. 3,178,821 demonstrates a modified ribbon arch bracket, but uses cutaway flanges to allow free tipping mesio-distally, deliberately avoiding any likelihood of restriction of tipping movement, (this movement enables easy correction of tooth crown position, but not root position). The Kesling bracket requires that an auxiliary be used such as the Kesling-Begg spring pin disclosed in British Patent Specification No. 1421601 to achieve correction of root position that is angulation.
This movement must be attained after the crown tipping, mentioned above, occurs.
It is an objective of the present invention to provide an orthodontic bracket of the arch-wire type seeking to overcome some of the abovementioned disadvantages in allowing for smooth rounded edges making for greater patient comfort and less resistance to the passage of food.
It is a further objective to provide an orthodontic bracket wherein the slot angulations are specific for each tooth and can be accurately achieved to the accuracy of a degree than ever could be obtained by adjustments to the prior art (known to me).
It is also an objective to provide an arch-wire slot built in the one-piece bracket.
It is a further objective to provide an orthodontic bracket of the arch-wire type wherein the arch-wire slot is pre-angulated in manufacture and does not require angulation correction.